Epidemiological model person, place & time

1. Epidemiological model person, place & time A.Prof. Dr. Maha A. AL-Nuaimi Ph.D. Com.Med.

2. Learning objectives Explain the descriptive epidemiology. Explain the essential characteristics of the person place and time model. Describe how the person place and time characterize the distribution of disease. Explain how the characteristics of person, place, & time are applied to formulate hypotheses about the possible source, modes of transmission and IP in acute disease outbreaks and chronic diseases.

3. The aims of epidemiology – Describe disease – Distribution, frequency – Identify etiological factors – Provide data for planning and implementation of control & preventive measures.

4. Case Scenario • If you are a responsible doctor in a village PHC, you noticed that there was an outbreak of disease characterized by: Fever and jaundice among the village pop. How you should describe the situation to the health authority.. ?

5. MODEL OF WHO, WHERE AND WHEN PLACE TIME PERSON Think of this as the standard dimensions used to track the occurrence of a disease.

6. Two broad types of epidemiology Descriptive epidemiology - Observation then description of the distribution of the disease in a population through PPT Model, to generate hypothesis about the disease determinants. Analytic epidemiology - Activities Testing a hypothesis about the cause of disease by studying the relationship between the disease and risk factors.

7. Descriptive Epidemiology • 3 essential characteristics of disease that we look for in descriptive studies: • Person …. Who gets the dis. • Place …. where • Time …. When • In sense, you are looking for .. why all of these people became ill. What do they have in common?

8. Person What kinds of people tend to develop a particular disease, and who tends to be spared? What’s unusual about those people? 8

9. Person Factors • Age, gender, race, ethnicity • Genetic predisposition • Concurrent disease • Diet, exercise, smoking • Risk taking behavior • SES, education, occupation 9

10. Personal factors Biological Trait (born with) … non-modifiable Social Trait (acquired) … modifiable What is The most important biologic trait that determines what disease an individual will contract ?? Why? Age, is directly related to the ability of the body to respond to disease, acquire immunity, and exposure., tissue response that reflex dis. Manifestation.

11. AGE Certain diseases are more frequent in certain age groups than others. Infectious diseases ?? Chronic and degenerative diseases ?? BIMODALITY .. ? Its imprtancs?

13. SEX Variations occur due to: 1) Biologic differences .. Sex linked dis. 2) Cultural and behavioral differences. .Sex predominant diseases. Lung Cancer 4:1 / M:F ..

15. OCCUPATION May alter the habit pattern of employees. Workers may exposed to certain risks. Coal miners …. Silicosis SOCIAL CLASS  Diseases show higher prevalence in upper class.. Certain Diseases more among low class.. BEHAVIOUR Smoking, sedentary life, over-eating, drug abuse ..

16. STRESS • Susceptibility to disease. • Exacerbation of symptoms. Migration Migration of people …. transmission of the disease.

17. Place • Where is the disease especially common or rare, and what is different about those places? • The association of the disease with place due to the present of etiology in inhabitants &/or in environment, • E.g.: major inhibitants in central Africa are sickle cell trait.. Why? 17

18. Geographic extent of a problem. Varied according:

19. INTERNATIONAL VARIATION CA stomach ….. in Japan VERSUS USA. NATIONAL VARIATION variations within countries. endemic Goitre, Malaria, Schistozomiasis… URBAN-RURAL VARIATIONS ?? LOCAL DISTRIBUTIONS ?? Spot Map Building Map

20. Spot map of deaths from cholera in Golden Square area, London, 1854clustering indicates what ???

21. Time Why does disease frequency change at that time or within that time?? 21

22. Time Factors Calendar Time / Time of Day Time since exposure Date of onset … what period?? Seasonality Temporal trends 22

23. Temporal Trends of Disease Occurrence • Cyclic trend (long term short term) • Periodic (short term) • Seasonal • Epidemic

24. Cyclic trends • Recurrent alterations in occurrence , interval or frequency of disease • Secular cyclicity(long term) • Levels of immunizations • Build up of susceptible • e.g. Hep A-7 yr cycle,Measles-2yr cycle • Short term cyclicity • Chickenpox, salmonella(yearly basis)

25. Secular Trend The long-time trend of disease occurrence

26. SHORT TERM CYCLICITY

27. Periodic Trend Temporal interruption of the general trend

28. Seasonal trend • Communicable diseases. measles and upper respiratory tract infections .. Winter. Typhoid, malaria, cholera … summer. • NCD seasonal variation ??

29. Seasonal Trend A cyclic variation in disease frequency by season

30. Epidemic: • An epidemic“a situation when the observed number of cases unaccountably exceeds the expected number” in specific place. • Comparison …….

31. Epidemic

32. Epidemic Classification 1- Common Source Epidemics • Point Source Epidemic • Continuous or intermittent. 2- Propagated Epidemics

33. 1- A Common source outbreak the affected individuals had an exposure to a common agent. • point source outbreak: - Single exposure, -One incubation period. - One peak epidemic curve. • Continuous exposure to source outbreak: - prolonged exposure. - more than one IP. - Irregular pattern curve (Rise but tails off gradually).

36. 2. Propagated (serial) outbreak: - a successive series of peaks - increasing no. of cases with each infected generation (IP) .. Successive peaks. . Decreased by ?? - gradual rise, peaks, gradual tail off. - person to person, arthropod vector

39. Types of disease occurrence Number of Cases of Disease Endemic:habitual presence of diseases within a given geographical area. Epidemic Time

40. Pandemic:a disease or condition that spreads across regions, countries and continents. • Sporadic the scattered presence of the disease within apop, • OutbreakOR clustering

41. SummeryPerson, Place & Time Is a descriptive model for any health problem or outbreak. Generate Hypotheses about the determinants of disease (risk factors), the Source, mode of transmission, possible IP. Applied mainly for CD and expanded to cover NCD.

42. THANK YOU